1. Field
The present inventive concept relates to a method and apparatus for outputting an audio signal. More particularly, the inventive concept relates to a method and apparatus for outputting an audio signal, whereby sound quality of the audio signal may be improved. The present inventive concept also relates to a method and apparatus for outputting an audio signal, whereby noise and errors that may occur during a switching amplification operation may be reduced.
2. Description of the Related Art
Class A, Class B, Class AB, and Class D amplifiers are used as audio power amplifiers that may output signals that may be recognized auditorily in response to audio signals. From among these amplifiers, the Class D amplifier is widely used because it reduces amplification efficiency degradation that occurs in the A-grade amplifier, the Class B amplifier, and the Class AB amplifier.
The Class D amplifier is a digital amplifier that converts an audio signal input in analog form into a digital signal, performs signal processing, such as noise elimination, or the like, on the digitally-converted audio signal, and amplifies the digitally-converted audio signal. The digitally-converted audio signal is amplified as a signal at a high voltage level. Here, the amplification operation is performed by a switching amplifier. Power at a high voltage level and a low voltage level is supplied to the switching amplifier. The switching amplifier performs a switching operation according to digital signals input to the switching amplifier, thereby outputting an audio signal at a high voltage level and an audio signal at a low voltage level, respectively.
The digital amplifier has high amplification efficiency. However, sound of the output audio signal is hard rather than soft. For example, ‘hard sound’ corresponds to mechanical sound or sounds having monotonous tone, and ‘soft sound’ corresponds to harmonic sound or sounds having mellow tone. In addition, simple distortion of sound may occur due to harmonic components generated by the digital amplifier.
In addition, when the switching operation is performed by the switching amplifier, switching noise occurs. Furthermore, the switching noise causes a reduction in a signal to noise ratio (SNR) of the switching amplifier. Also, power noise, such as ripple, exists in the power supplied to the switching amplifier. The power noise also causes a reduction in the SNR. In addition, a switching loss that occurs during switching amplification and a delay of a falling and rising time of a switching driving signal cause non-linearity of the output audio signal.
Thus, a method and apparatus that may solve the problems relating to monotonous sound, a reduction in the SNR, and non-linearity needs to be provided.